Technical Field
This disclosure relates to the bonding, attachment or coupling of structures having different physical characteristics, such as the bonding of a composite structure to a metallic structure. More specifically, this disclosure relates to turbomachinery, more particularly, to various means for bonding composite fan blades or vanes to metallic or composite rotors or hubs.
Description of the Related Art
Turbomachinery fan blades may be secured to a supporting rotor by providing shaped slots in the rotor that mateably receive correspondingly shaped roots of the fan blades. For example, the rotors may include dovetail or fir tree shaped slots that receive complementary shaped roots disposed at the radially inwardly ends of the fan blades. The slots of the rotor and the roots of the fan blades are adapted to lock the fan blades against radial movement as the rotor spins about its axis.
Designers of gas turbine engines are constantly seeking ways to reduce the weight of various components. One strategy involves the substitution of traditional titanium and aluminum alloys as primary construction materials in favor of various composite materials. Composites are attractive because they are typically lighter than titanium or aluminum alloys and exhibit high specific strength and stiffness. Polymer matrix composites may be used for many gas turbine engine parts despite their inability to withstand high temperatures. For example, carbon fiber reinforced polymer composites have been successfully used in the fabrication of fan blades. Metal matrix composites and ceramic matrix composites exhibit lower specific strengths, but show promise as they are able to withstand higher temperatures.
While the design and development of composite fan blades for gas turbine engines is under way, the rotors to which fan blades are attached are still primarily fabricated from metal alloys. However, the use of composite materials for rotors of fan assemblies is on the horizon. Regardless, because of different structural requirements, fan blades and rotors will most likely continue to be fabricated from different materials having different properties. In the case of a composite fan blade and a rotor, a problem arises because of the different material properties of the composite used to fabricate the fan blade and the metal alloy or composite material used to fabricate the rotor. When materials of different characteristics are coupled together, it may be difficult to provide robust attachment method because, amongst other reasons, differences in the coefficients of thermal expansion (CTEs) can compromise the connection between the fan blades and the rotor.
Thus, there is a need for improved techniques for bonding, coupling or attaching a composite structure, such as a composite fan blade, to a structure made from a different material, such as a metallic rotor or a composite rotor. While this disclosure utilizes fan blades and rotors as a primary example, this disclosure is directed more broadly to methods of bonding, coupling, or connecting one structure to another structure, wherein the structures are made from different materials having different material properties.